1. Field of the Invention
The present invention relates in general to a diamond-coated body, and more particularly to such a diamond-coated body in which a diamond coating is fixed to a substrate with a sufficiently high strength even where the substrate is made of a super-fine particle cemented carbide with a high Co content, and also to a method of manufacturing the same.
2. Discussion of the Related Art
As one type of a cutting tool such as an end mill, a tap and a drill, there is proposed a diamond-coated cutting tool in which a tool substrate made of a cemented carbide is coated with a diamond coating. In a process of formation of the diamond coating on the tool substrate in accordance with a CVD (chemical vapor deposition) method or other method, at a raised temperature of 700-1000xc2x0 C., Co (cobalt) contained in the cemented carbide is separated from the tool substrate due to the raised temperature so that diamond particles of the diamond coating are graphitized. Such graphitization of the diamond particles undesirably reduces an adhesive or bonding strength with which the diamond coating is bonded to the tool substrate. In the interest of avoiding the separation of the Co from the tool substrate, the tool substrate is commonly subjected to an acid treatment in which Co adjacent to the surface of the substrate is removed by using a suitable acid such as sulfuric acid or nitric acid, prior to the formation of the diamond coating on the substrate. However, where the substrate is made of a super-fine particle cemented carbide having high a Co content, even if Co adjacent to the surface of the substrate has been completely removed from the substrate, Co contained in the substrate comes to the surface of the substrate in a large amount during the heating of the diamond coating. Thus, it is not possible to avoid the reduction in the strength of bonding of the diamond coating to the substrate, making it impossible to use, as the material of the tool substrate, the super-fine particle cemented carbide which inherently has a higher degree of toughness or unbrittleness owing to its high Co content, than the other cemented carbide, and which is advantageously used as the material of the substrate of the cutting tool serving to cut particularly a cast iron or other hard materials.
JP-B2-6-951 (publication of examined Japanese Patent Application laid open in 1994) discloses a diamond-coated body including a substrate, a crystalline diamond coating, an interface layer which is made of TiC or other material, and a layer which has a non-crystalline carbonized structure. In this diamond-coated body, the interface layer is disposed on the substrate, and the non-crystalline carbonized structure layer is disposed on the interface layer so as to be interposed between the interface layer and the diamond coating. This arrangement makes it possible to use, as the material of the substrate, the super-fine particle cemented carbide having a high Co content.
However, in manufacturing the above-described diamond-coated body, it is necessary to implement a step of forming the non-crystalline carbonized structure layer on the interface layer prior to the formation of the crystalline diamond coating. This extra step requires a cumbersome operation, increasing the manufacturing cost.
The above-described drawbacks or problems are encountered not only where the diamond-coated tool takes the form of a cutting tool but also where the diamond-coated tool takes the form of other machining tools such as a cold-forming tool which is designed to form the workpiece into a desired shape by plastically deforming the workpiece.
It is therefore a first object of the present invention to provide a diamond-coated body in which a diamond coating is fixed to a substrate with a sufficiently high strength even where the substrate is made of a super-fine particle cemented carbide with a high Co (cobalt) content. This first object may be achieved according to any one of first through eleventh aspects of the invention which are described below.
It is a second object of the invention to provide a method of manufacturing a diamond-coated body in which a diamond coating is fixed to a substrate with a sufficiently high strength even where the substrate is made of a super-fine particle cemented carbide with a high Co content. This second object may be achieved according to either of twelfth and thirteenth aspects of the invention which are described below.
The first aspect of this invention provides a diamond-coated body comprising: a substrate made of a cemented carbide; a diamond coating; and an interface layer interposed between the substrate and the diamond coating, wherein the interface layer consists of a solid solution including an aluminum nitride and a metal which belongs to one of groups IVa, Va and VIa of the periodic table. It is noted that the diamond-coated body of the invention can be also interpreted to comprise the above-described substrate, and a multilayer coating which covers the substrate and which includes the above-described diamond coating as its outer layer and the above-described interface layer as its inner layer. In other words, the diamond coating and the interface layer can be also interpreted to cooperate with each other to provide a multilayer coating which covers the substrate. It is further noted that the above-described interface layer can be also referred to as an intermediate layer.
According to the second aspect of the invention, in the diamond-coated body defined in the first aspect of the invention, the diamond coating is held in contact with the interface layer. The crystalline diamond coating is disposed directly on an outer surface of the interface layer, without a layer consisting of a non-crystalline carbonized structure which is conventionally provided to be interposed between the interface layer and the diamond coating, as discussed above in Discussion of the Related Art.
According to the third aspect of the invention, in the diamond-coated body defined in the first or second aspect of the invention, the interface layer includes one of TiAlN (aluminum titanium nitride), CrAlN (aluminum chromium nitride) and VAlN (aluminum vanadium nitride), and is formed on a surface of the substrate in accordance with a physical vapor deposition method. It is noted that TiAlN is interpreted to mean a solid solution including an aluminum nitride and Ti, that CrAlN is interpreted to mean a solid solution including an aluminum nitride and Cr, and that VAlN is interpreted to mean a solid solution including an aluminum nitride and V.
According to the fourth aspect of the invention, in the diamond-coated body defined in any one of the first through third aspects of the invention, the substrate is made of a super-fine particle cemented carbide which includes WC (tungsten carbide) as a main component thereof, the super-fine particle cemented carbide further including Co such that a content of Co therein is 3-25 wt %.
According to the fifth aspect of the invention, in the diamond-coated body defined in the fourth aspect of the invention, the content of Co in the super-fine particle cemented carbide is 5-10 wt %.
According to the sixth aspect of the invention, in the diamond-coated body defined in the fourth aspect of the invention, the super-fine particle cemented carbide includes a hard phase which is provided by particles whose average diameter is not larger than 1 xcexcm.
According to the seventh aspect of the invention, in the diamond-coated body defined in any one of the first through sixth aspects of the invention, the substrate has pits and projections formed on a surface thereof such that the surface of the substrate has a roughness curve whose maximum height Ry is within a range from 0.5 xcexcm to 2 xcexcm.
According to the eighth aspect of the invention, in the diamond-coated body defined in the seventh aspect of the invention, the interface layer is held in contact with the surface of the substrate which has the roughness curve, and wherein the interface layer has a thickness ranging from 0.5 xcexcm to 5 xcexcm.
According to the ninth aspect of the invention, in the diamond-coated body defined in any one of the first through eighth aspects of the invention, the diamond coating has a thickness ranging from 5 xcexcm to 20 xcexcm.
According to the tenth aspect of the invention, in the diamond-coated body defined in any one of the first through ninth aspects of the invention, the diamond-coated body consists of a machining tool which is to be moved relative to a workpiece, for thereby machining the workpiece.
According to the eleventh aspect of the invention, in the diamond-coated body defined in the tenth aspect of the invention, the machining tool consists of an end mill.
The twelfth aspect of the invention provides a method of manufacturing a diamond-coated body comprising (a) a substrate made of a cemented carbide, (b) a diamond coating, and (c) an interface layer interposed between the substrate and the diamond coating, the method comprising: a surface roughening step of roughening a surface of the substrate such that the roughened surface has pits and projections formed thereon; an interface-layer forming step of forming the interface layer out of one of TiAlN, CrAlN and VAlN in accordance with a physical vapor deposition method, such that the interface layer is held in contact in an inner surface thereof with the roughened surface of the substrate having the pits and projections; and a diamond-coating forming step of forming the diamond coating in accordance with a chemical vapor deposition method, such that the diamond coating is held in contact with an outer surface of the interface layer.
According to the thirteenth aspect of the invention, in the method defined in the twelfth aspect of the invention, the surface of the substrate is roughened to have pits and projections such that the surface of the substrate has a predetermined degree of surface roughness, and wherein a thickness of the interface layer is determined on the basis of the predetermined degree of surface roughness of the surface of the substrate such that the pits and projections of the surface of the substrate cause the outer surface of the interface layer to have pits and projections.
In the diamond-coated body defined in any one of the first through eleventh aspects of the invention, the interface layer consists of the solid solution including the aluminum nitride and the metal (e.g., Ti (titanium), Cr (chromium) and V (vanadium)) which belongs to one of the groups IVa, Va and VIa of the periodic table. Owing to the provision of the thus constructed interface layer on the surface of the substrate, the diamond coating can be fixed to the substrate through the interface layer with a sufficiently large adhesive or fixing strength, even in the absence of a layer having a non-crystalline carbonized structure. This arrangement contributes to simplification of the construction of the diamond-coated body and accordingly reduction of the cost of manufacture of the diamond-coated body. It can be assumed that the fixing strength is increased by so-called xe2x80x9cdropletsxe2x80x9d, i.e., small pits and projections which are likely to be formed in the outer surface of the interface layer, for example, where the interface layer is formed of TiAlN in accordance with a physical vapor deposition (PVD) method. That is, the small pits and projections are effective to increase an area of the outer surface of the interface layer which can be held in contact with the diamond coating, and to enable the interface layer to be brought into engagement in its pits and projections with the diamond coating.
The interface layer interposed between the substrate and the diamond coating further contributes to prevent Co contained in the substrate from being separated from the substrate during the formation of the diamond coating, avoiding a risk of reduction in the fixing strength with which the diamond coating is fixed to the interface layer and the substrate, and accordingly making it possible to eliminate an acid treatment or other treatment for removing Co from the substrate, prior to the formation of the diamond coating. Namely, the interface layer and the diamond coating can be fixed to the substrate with the sufficiently high fixing strength, not only where the substrate is made of the ordinary cemented carbide but also where the substrate is made of the super-fine particle cemented carbide having a high Co content. Therefore, in the diamond-coated body of the invention, the super-fine particle cemented carbide may be used as a material for forming the substrate. Where a machining tool is provided by the diamond-coated body including the substrate made of the super-fine particle cemented carbide, the machining tool can be advantageously used to machine or cut a workpiece made of a hard material such as a cast iron and an aluminum alloy casting containing high silicon, with its remarkably improved durability owing to a high degree of wear resistance of the diamond coating and a high degree of unbrittleness of the super-fine particle cemented carbide.
The manufacturing method defined in either of the twelfth and thirteen aspects of the invention provides substantially the same technical advantages as the diamond-coated body defined in any one of the first through eleventh aspects of the invention.
The diamond-coated body of the present invention may be a diamond-coated machining tool, such as an end mill, a drill, a tap, a threading die, a replaceable insert which is fixed to a tool holder used for a lathe cutting or milling operation, a cold-forming tool which is designed to form a workpiece into a desired shape by plastically deforming the workpiece, and any other machining tools each of which is to be moved relative to a workpiece for thereby machining the workpiece. In addition, the diamond-coated body of the invention may be other than such machining tools. The machining tool provided by the diamond-coated body of the invention is advantageously used to machine, particularly, a workpiece made of a hard material, and is capable of exhibiting an remarkably improved durability.
The technical advantages of the present invention can be enjoyed, particularly, where the substrate is made of the super-fine particle cemented carbide which has a high Co content. However, the principle of the invention may be applied to the diamond-coated body in which the substrate is made of an ordinary cemented carbide.
The interface layer preferably includes one of TiAlN, CrAlN and VAlN, more preferably includes TiAlN. Where the substrate has the pits and projections formed on its surface, for example, by roughening the substrate surface, the thickness of the interface layer is determined on the basis of the degree of the surface roughness of the substrate surface such that the pits and projections of the substrate surface cause the outer surface of the interface layer to have pits and projections. In this instance, the outer surface of the interface layer does not have to have the same roughness curve as the substrate surface. Namely, the pits and projections of the outer surface of the interface layer does not have to have a profile identical with that of the pits and projections of the substrate surface. The thickness of the interface layer preferably ranges from 0.5 xcexcm to 5 xcexcm, while the maximum height Ry of the roughness curve of the substrate surface is preferably within a range from 0.5 xcexcm to 2 xcexcm. The thickness of the diamond coating preferably ranges from 5 xcexcm to 20 xcexcm, more preferably ranges from 10 xcexcm to 15 xcexcm, although the optimum range of the thickness of the diamond coating varies depending upon the material of the interface layer and the surface roughness of the outer surface of the interface layer.
In the surface roughening step in the twelfth aspect of the invention, the substrate surface is roughed, preferably, by an electrolytic polishing or other chemical corrosion treatment, or by a sandblasting with abrasive grains made of SiC or other materials.
In the interface-layer forming step in the twelfth aspect of the invention, the interface layer is formed in accordance with a PVD method such as sputtering method, ion plating method and other vacuum vapor deposition method. However, the interface layer may be formed by other coating method, depending upon the material forming the interface layer.
In the diamond-coating forming step in the twelfth aspect of the invention, the diamond coating is formed, preferably, in accordance with a CVD method such as a microwave plasma CVD method and a hot filament CVD method. However, the diamond-coating forming step may be implemented by using the other method such as a high-frequency plasma CVD method.